Cleaning resin composition

ABSTRACT

A resin composition for cleaning the inside of molding machines, capable of easily achieving the color exchange and resin exchange of thermoplastic resins in various molding machines, in a small quantity, by a simple operation and in a short time is provided, which resin composition is a cleaning resin composition having (a) 1-10 wt. % of a polystyrene resin, 1-20 wt. % of a neutral salt of an alkylbenzenesulfonic acid, 1-30 wt. % of an inorganic filler and 0.5-10 wt. % of a water-repellent compound blended with a high density polyethylene resin having a melt index of 1.0 or less and a Q value expressing a molecular weight distribution, of 10 or less.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a cleaning resin composition used for cleaningthe inside of various molding machines.

More particularly it relates to a cleaning resin composition havingdefinite quantities of a polystyrene resin, a neutral salt of analkylbenzenesulfonic acid, an inorganic filler and a water-repellentcompound, blended with a high density polyethylene resin having a highviscoelasticity when melted and a narrow molecular weight distribution,and a cleaning resin composition having a low molecular weightpolyethylene wax, a neutral salt of an alkylbenzenesulfonic acid and aninorganic filler, blended with a high density polyethylene resin havinga high viscoelasticity when melted and a narrow molecular weightdistribution.

2. Description of the Related Art

In the field of mold processing of plastics, production of more gradesin smaller quantities has been intended. Further, due to the creation ofhigh-performance engineering plastics, the frequency of color exchangeor resin exchange inside molding machines has rapidly increased.

Heretofore, at the time of such color exchange or resin exchange, inorder to remove contaminants caused by the preceding resin inside themolding machine, the following processes have been employed:

a process of drawing out the contaminated screw inside the moldingmachine, followed by brushing the screw or the inner wall of thecylinder to thereby clean them, or a process of flowing a colorlessresin as a cleaning resin through the inside of the cylinder to cleanthe screw together with the cylinder, without drawing out the screw.

However, both of these processes require a long time to completely cleanthe screw and the inside of the molding machine, and in the case ofco-cleaning, a large quantity of cleaning resin is required resulting ina large loss in economical and time aspects.

Thus, in order to solve such problems, various cleaning agents forcleaning the inside of molding machines have been developed.

For example, a cleaning agent composed mainly of an acrylic resin, acleaning agent obtained by blending a surfactant with a thermoplasticresin (Japanese patent application laid-open No. Sho 59-124999), acleaning agent obtained by blending a surfactant and a lubricant such asa metal salt of stearic acid with a thermoplastic resin (Japanese patentapplication laid-open No. Sho 58-149998) and a composition obtained byblending a sodium alkylbenzenesulfonate, talc, zinc stearate, etc. witha linear, low density polyethylene (Japanese patent applicationlaid-open No. Sho 60-139411) have been proposed.

However, in the case of the cleaning agent composed mainly of an acrylicresin, since the acrylic resin has a high melt viscosity, a high load isapplied to the molding machine at the time of cleaning and also when thetemperature inside the molding machine is raised in order to lower themelt viscosity, there is a drawback that the acrylic resin issusceptible to thermal decomposition.

Further, there are drawbacks that operations are troublesome and timeconsuming. For example, before the cleaning agent is used, the die,metal gauze, etc. of the molding machine have to be removed, and furtherif the cleaning agent remains inside the molding machine aftercompletion of the cleaning, the remaining cleaning agent mixes in thesucceeding molded product so that the agent in the form of foreignmatter deteriorates the appearance or the physical properties of themolded product.

Further, in the cases of a cleaning agent obtained by blending asurfactant with a thermoplastic resin and a cleaning agent obtained byfurther blending a metal stearate, etc. therewith, when the servicetemperature of these cleaning agents reaches about 250° C. or higher, agas is generated from decomposition of the cleaning agents so that ithas a bad effect upon the operational environment and at the same time,the cleaning effect of the cleaning agent is still insufficient.Further, in the case of the cleaning agent obtained by blending a sodiumalkylbenzenesulfonate, talc, etc. with a linear low densitypolyethylene, since the agent has a low viscoelasticity when meltedinside the molding machine, the capability of removing the precedingresin i.e., the cleanability is low, and in the case where the quantityof the inorganic filler blended is large, the cleaning agent itself isliable to remain on the inside wall of the molding machine so that inorder to remove the remaining cleaning agent, a large quantity of thecleaning resin has to be used.

Further, the present inventors have previously proposed a thermoplasticresin composition obtained by blending a neutral salt of analkylbenzenesulfonic acid and a water-repellent compound with athermoplastic resin (Japanese patent application laid-open No. Sho62-195045), but a cleaning agent having a further superior cleanabilityhas been desired.

SUMMARY OF THE INVENTION

The present inventors have conducted extensive research in order toobtain a resin composition for cleaning the insides of molding machines,capable of easily achieving the color exchange and the resin exchange ofthermoplastic resins in various molding machines, using small quantityof the cleaning resin composition, by a simple operation and in a shorttime.

As a result, we have found that a composition obtained by blending smallquantities of a polystyrene resin, a neutral salt of analkylbenzenesulfonic acid, an inorganic filler and a water-repellentcompound with a high density polyethylene resin having a highviscoelasticity when melted and a narrow molecular weight distribution,and a composition obtained by blending a low molecular weightpolyethylene wax, a neutral salt of an alkylbenzenesulfonic acid thealkyl group of which has 10 to 18 carbon atoms and an inorganic fillerwith a high density polyethylene resin having a high viscoelasticitywhen melted and a narrow molecular weight distribution are each acleaning resin composition exhibiting a notably improved cleaningeffect, and have completed the present invention based upon the abovefinding.

The present invention includes the following compositions (1) and (2) inthe first aspect and (3) and (4) in the second aspect:

(1) A cleaning resin composition having 1 to 10% by weight of apolystyrene resin, 1 to 20% by weight of a neutral salt of analkylbenzenesulfonic acid, 1 to 30% by weight of an inorganic filler and0.5 to 10% by weight of a water-repellent compound, blended with a highdensity polyethylene resin having a melt index of 1.0 or less and a Qvalue expressing a molecular weight distribution, of 10 or less, thetotal % by weight of the composition being 100.

(2) A cleaning resin composition according to item (1) which is furthermelt-kneaded and molded into a pellet form.

(3) A cleaning resin composition having 1 to 10% by weight of apolyethylene wax, 1 to 20% by weight of a neutral salt of analkylbenzenesulfonic acid in which the alkyl group has 10 to 18 carbonatoms and 1 to 20% by weight of an inorganic filler, with a high densitypolyethylene resin having a melt index of 1.0 or less and a Q valueexpressing a molecular weight distribution, of 10 or less, the total %by weight of the composition being 100.

(4) A cleaning resin composition according to item (3) which is furthermelt-kneaded and molded into a pellet form.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

As the high density polyethylene resin used in the present invention, anethylene homopolymer, copolymers of ethylene with propylene, butene-1,hexene-1, etc. and the like, each having a melt index of 1.0 or less anda Q value expressing a molecular weight distribution, of 10 or less,preferably 8 or less are mentioned.

The Q value referred to herein means a numeral value obtained bymeasuring the number average molecular weight (Mn) and the weightaverage molecular weight (Mw) employing gel permeation chromatography(GPC) in a conventional manner and expressed in terms of Q=Mw/Mn.

If the melt index of the high density polyethylene resin exceeds 1, themelt fluidity of the resulting cleaning resin composition inside themolding machine is too high when the inside of the molding machine iscleaned with the cleaning resin composition, so that the capability ofcleaning the preceding resin remaining inside the molding machine, i.e.cleanability is reduced. On the other hand, if a high densitypolyethylene resin having a broad molecular weight distribution (Qvalue: higher than 10) is used, the viscoelasticity of the resultingcleaning resin composition when melted is low when the inside of themolding machine is cleaned with the cleaning resin composition so thatthe cleanability is reduced. As the polystyrene resin used in thepresent invention, commercially available, conventional polystyreneresin or high-impact polystyrene resin may be used, and the quantity ofthe polystyrene resin blended is 1 to 10% by weight based on the weightof the composition. If the blended quantity is less than 1% by weight,the effect of cleaning the inside of the molding machine is small, whileif it exceeds 10% by weight, the compatibility of the resin with thehigh density polyethylene is inferior so that when a pellet formcomposition is produced, it is impossible due to grinding, etc. toobtain a pellet form cleaning resin composition in a uniform form.

The molecular weight of the polyethylene wax used in the presentinvention has no particular limitation, but the molecular weight ispreferably 1,000 to 10,000. Further, the quantity of the polyethylenewax blended is preferably 1 to 10% by weight. If the blended quantity isless than 1% by weight, the lubricating properties of the cleaning resincomposition inside the molding machine are reduced so that it isdifficult to remove the remaining resin by the succeeding cleaningresin, while if it exceeds 10% by weight, to the contrary, thelubricating properties are too enhanced so that the cleanability isreduced.

As the neutral salt of an alkylbenzenesulfonic acid used in the presentinvention, Na salt, Ca salt, Mg salt, K salt, etc. of analkylbenzenesulfonic acid in which the alkyl group has 6 to 20 carbonatoms, preferably 10 to 18 carbon atoms, are mentioned. The quantity ofthe neutral salt of an alkylbenzenesulfonic acid blended is 1 to 20% byweight, preferably 5 to 15% by weight. If the blended quantity is lessthan 1% by weight. the cleanability inside the molding machine is notexhibited, while if it exceeds 20% by weight, the neutral salt of analkylbenzenesulfonic acid remains inside the molding machine and themelt fluidity of the cleaning resin composition at the time of cleaningis inferior, so that it is necessary to apply a high load to the moldingmachine.

As the inorganic filler used in the present invention, inorganic fillersusually blended with polyolefin resins e.g.,

MgCO₃, CaCO₃, talc, CaSO₄, magnesium silicate, silica, alumina, etc. maybe used. The inorganic filler contained in the cleaning resincomposition exerts a function of scraping off dirt inside the moldingmachine and the preceding resin adhered to the machine by mechanicalforce. The quantity of the inorganic filler blended is 1 to 30% byweight, preferably 5 to 20% by weight based on the weight of thecomposition in the case of the first aspect of the present invention. Ifthe blended quantity is less than 1% by weight, the cleaning effect isinsufficient, while if it exceeds 30% by weight, the melt fluidity ofthe cleaning resin composition is reduced so that too high a load isapplied to the molding machine at the time of cleaning. Further, in thecase of the second aspect of the present invention, the quantity of theinorganic filler blended is 1 to 20% by weight, preferably 3 to 15% byweight. If the blended quantity is less than 1% by weight, thecleanability is insufficient, while if it exceeds 20% by weight, to thecontrary, the melt fluidity of the cleaning resin composition isreduced; hence too high a load is applied to the molding machine at thetime of cleaning or the cleaning resin composition remains inside themolding machine to make the substitution of the composition by thesucceeding cleaning resin difficult.

As the water-repellent compound used in the present invention, syntheticwaxes such as polyethylene wax, etc., silicone, wax, metal salts ofhigher fatty acids such as calcium stearate, zinc stearate, leadstearate, etc., and mixtures of two or more kinds of the foregoing maybe mentioned. The quantity of the water-repellent compound blended is0.5 to 10% by weight, preferably 2 to 10% by weight. The water-repellentcompound contained in the cleaning resin composition of the presentinvention exerts a lubricating function. If the quantity of thewater-repellent compound blended is less than 0.5% by weight, itslubricating effect is small, while if it exceeds 10% by weight, thelubricating properties are too enhanced, so that the mechanical force ofthe coexisting inorganic filler inside the molding machine is reduced,resulting in reduction of the cleanability.

Besides, in the cleaning resin composition in the second aspect of thepresent invention, it is possible, if desired, to use a water-repellentcompound such as waxes e.g. polypropylene wax, carnauba wax, etc.,silicone, paraffin wax, metal salts of higher fatty acids e.g. calciumstearate, magnesium stearate, etc.

In the compositions of the present invention, antioxidants, usuallyblended with polyolefin resins, such as phenolic antioxidants, thioantioxidants, phosphorus antioxidants, etc., may be blended.

Besides, in the compositions of the present invention, it is possible,if desired, to blend a surfactant such as sodium alkyl ether sulfateesters in which the alkyl group has 6 to 20 carbon atoms, sodiumα-olefinsulfonate, fatty acid alkanol amides, sulfonic acid chloride,etc.

The composition in the first aspect of the present invention is obtainedby feeding definite quantities of a high density polyethylene resinhaving a melt index of 1.0 or less and a Q value of 10 or less, apolystyrene resin, a neutral salt of an alkylbenzenesulfonic acid, aninorganic filler and a water-repellent compound and at least one of theabove-mentioned antioxidants into an agitating and mixing apparatus suchas a Henschel mixer (tradename), supermixer, etc., and mixing them withstirring for 1 to 5 minutes, and it is also possible to obtain thecomposition in the form of pellets by extruding the above mixture bymeans of a single-screw extruder or a twin-screw extruder at amelt-kneading temperature of 180° to 230° C.

The cleaning resin composition in the second aspect of the presentinvention is obtained by feeding definite quantities of a high densitypolyethylene having a melt index of 1.0 or less and a Q value of 10 orless, a polyethylene wax, a neutral salt of an alkylbenzenesulfonic acidin which the alkyl group has 10 to 18 carbon atoms and an inorganicfiller into an agitating and mixing apparatus such as a Henschel mixer(tradename) and mixing them with stirring for 1 to 5 minutes, and it isalso possible to obtain the composition in the form of pellets bymelt-kneading the above mixture at a melt-kneading temperature of 180°to 230° C., by means of a single-screw or twin-screw extruder.

The present invention will be described in more detail by way of theexamples and comparative examples, but it should not be construed to belimited thereto.

(1) The cleanability test in the examples and comparative examples wascarried out according to the following method:

Black pellets of acrylonitrile-butadiene-styrene resin (ABS resin)containing 1% by weight of carbon black or black pellets of modifiedpolyphenylene oxide were injection-molded by means of a 35 tonsinjection molding machine in 15 shots, followed by injection-molding therespective cleaning resin compositions obtained in the examples andcomparative examples, each in 100 g, to thereby clean the inside of themolding machine, repeating the injection molding with the respectivecleaning resins till the resulting molded products appeared colorlessand determining the respective quantities of the cleaning resinsrequired therefor and also measuring the respective cleaning times inwhich the molded products appeared colorless, as cleaning time.

(2) Measurement according to GPC was carried out under the followingconditions:

    ______________________________________                                        Apparatus:                                                                              GPC 150 C manufactured by Waters Co., Ltd.                          Column:   TSK-GEL GMH 6-HT made by                                                      TOSOH CORPORATION                                                   Solvent:  ODCB (o-dichlorobenzene)                                            Temperature:                                                                            135° C.                                                      Flow rate:                                                                              1.0 ml/min                                                          ______________________________________                                    

In addition, the Q value employed as a measure of molecular weightdistribution is expressed by the following equation:

EXAMPLE 1

A high density polyethylene having a melt index (measured according toJIS K 6760) of 0.3, a Q value of 6.7 and a density of 0.945 (3.025 Kg),a polystyrene having a melt index (measured according to JIS K 6871) of20 (0.40 Kg), magnesium dodecylbenzenesulfonate (0.25 Kg), calciumcarbonate (1.25 Kg) and a polyethylene wax (number average molecularweight: 1,500) (0.075 Kg) were placed in a 20 l capacity Henschel mixer(tradename), followed by mixing these with stirring at a revolutionnumber of 500 rpm for 3 minutes, feeding the resulting mixture into ahopper of a single-screw extruder of 35 mm in cylinder diameter,extruding strands under conditions of a cylinder temperature of 200° C.and a die temperature of 190° C. and cutting the strands by means of apelletizer to obtain a pellet-form composition. Next, a black ABS resincontaining 1% by weight of carbon black was injection-molded by means ofan injection molding machine heated to a cylinder temperature of 230° C.in 15 shots, followed by cleaning the inside of the molding machine with100 g of the composition of the present invention (described immediatelyabove), thereafter feeding an uncolored polypropylene resin (melt flowrate according to JIS K 6758: 20) as a cleaning resin into the moldingmachine, repeating injection molding to clean the inside of the moldingmachine and continuing this operation until the resulting molded productwas not colored.

The quantity of the polypropylene resin required for the cleaning was100 g, the number of shots was 5 and the cleaning time was 10 minutes.

EXAMPLE 2

Mixing and pelletizing were carried out in the same manner as in Example1 except that a high density polyethylene having a melt index of 0.45, aQ value of 6.6 and a density of 0.945 was used, to obtain a cleaningresin composition. This composition was subjected to a cleanability testin the same manner as in Example 1. The quantity of the polypropyleneresin used as the cleaning resin was 120 g, the number of shots was 6and the cleaning time was 11 minutes.

EXAMPLE 3

Mixing and pelletizing were carried out in the same manner as in Example1 except that a high density polyethylene having a melt index of 0.8, aQ value of 6.4 and a density of 0.945 was used, to obtain a cleaningresin composition. This composition was subjected to a cleanability testin the same manner as in Example 1. The quantity of the polypropyleneresin used as a cleaning resin was 120 g, the number of shots was 6 andthe cleaning time was 11 minutes.

EXAMPLE 4

A high density polyethylene having a melt index of 0.45, a Q value of6.6 and a density of 0.945 (3.70 Kg), a polystyrene having a melt indexof 20 (1.0 Kg), magnesium dodecylbenzenesulfonate (0.75 Kg), calciumcarbonate (0.25 Kg) and a polyethylene wax (0.20 Kg) were mixed andpelletized in the same manner as in Example 1.

Next, a modified polyphenylene oxide containing 1% by weight of carbonblack was injection-molded by means of an injection molding machineheated to a cylinder temperature of 300° C. in 15 shots, followed byinjection-molding 100 g of the composition of the present invention toclean the inside of the molding machine and then carrying out acleanability test in the same manner as in Example 1, using apolyethylene terephthalate (FRPET C3030 made by Teijin Ltd.) as acleaning resin. The quantity of the polyethylene terephthalate used as acleaning resin was 260 g, the number of shots was 13 and the cleaningtime was 19 minutes.

COMPARATIVE EXAMPLE 1

Mixing and pelletizing were carried out in the same manner as in Example1 except that a high density polyethylene having a melt index of 5.0, aQ value of 7.5 and a density of 0.945 (3.025 Kg) was used, to obtain acleaning resin composition. This composition was subjected to acleanability test in the same manner as in Example 1. The quantity of apolypropylene resin used as a cleaning resin was 400 g, the number ofshots was 20 and the cleaning time was 25 minutes.

COMPARATIVE EXAMPLE 2

Mixing and pelletizing were carried out in the same manner as in Example1 except that a high density polyethylene having a melt index of 0.30, aQ value of 15.7 and a density of 0.945 (3.025 Kg) was used, to obtain acleaning resin composition. This composition was subjected to acleanability test in the same manner as in Example 1. The quantity of apolypropylene resin used as a cleaning resin was 520 g, the number ofshots was 26 and the cleaning time was 31 minutes.

COMPARATIVE EXAMPLE 3

Mixing and pelletizing were carried out in the same manner as in Example1 except that a low density polyethylene (melt index: 58, a Q value:8.7, a density: 0.927) (3.025 Kg) was used, to obtain a cleaning resincomposition. This composition was subjected to a cleanability test inthe same manner as in Example 1. The quantity of a polypropylene resinused as a cleaning resin was 500 g, the number of shots was 25 and thecleaning time was 30 minutes.

COMPARATIVE EXAMPLE 4

Mixing and pelletizing were carried out in the same manner as in Example1 except that a high density polyethylene having a melt index of 0.80, aQ value of 6.4 and a density of 0.945 (3.425 Kg) was used and apolystyrene resin was not used, to obtain a cleaning resin composition.This composition was subjected to a cleanability test in the same manneras in Example 1. The quantity of a polypropylene resin used as acleaning resin was 460 g, the number of shots was 23 and the cleaningtime was 28 minutes.

COMPARATIVE EXAMPLE 5

Mixing and pelletizing were carried out in the same manner as in Example1 except that a linear low density polyethylene (melt index: 1.5, Qvalue: 11.3, a density: 0.920) (2.1 Kg), magnesiumdodecylbenzenesulfonate (0.20 Kg), calcium carbonate (2.50 Kg), sodiumstearate (0.10 Kg) and zinc stearate (0.10 Kg) were used, to obtain acleaning resin composition. This composition was subjected to acleanability test in the same manner as in Example 1. The quantity of apolypropylene resin used as a cleaning resin was 460 g, the number ofshots was 23 and the cleaning time was 28 minutes.

COMPARATIVE EXAMPLE 6

Mixing and pelletizing were carried out in the same manner as inComparative example 5 except that a high density polyethylene (meltindex: 5.0, Q value: 7.5 and density: 0.945) (2.1 Kg) was used, toobtain a cleaning resin composition. This composition was subjected to acleanability test in the same manner as in Example 1. The quantity of apolypropylene resin used as a cleaning resin was 420 g, the number ofshots was 21 and the cleaning time was 26 minutes.

COMPARATIVE EXAMPLE 7

Mixing and pelletizing were carried out in the same manner as in Example1 except that a high density polyethylene (melt index: 5.0, Q value: 7.5and density: 0.945) (1.90 Kg), calcium carbonate (2.50 g), liquidparaffin (0.50 Kg) and ethylenebishydroxystearic acid amide (0.10 Kg)were used, to obtain a cleaning resin composition. This composition wassubjected to a cleanability test in the same manner as in Example 1. Thequantity of a polypropylene resin used as a cleaning resin was 840 g,the number of shots was 42 and the cleaning time was 47 minutes.

The compositions and the cleanability test results of the respectivecompositions of Examples 1-4 and Comparative examples 1-7 arecollectively shown in Table 1.

                                      TABLE 1                                     __________________________________________________________________________               Example         Comparative example                                Item       1   2   3   4   1   2   3   4   5   6   7                          __________________________________________________________________________    Composition (wt. %)                                                           Kind MI Q                                                                     Polyethylene                                                                  HDPE 0.30                                                                             6.7                                                                              60.5                                                                              --  --  --  --  --  --  --  --  --  --                         HDPE 0.45                                                                             6.6                                                                              --  60.5                                                                              --  74.0                                                                              --  --  --  --  --  --  --                         HDPE 0.80                                                                             6.4                                                                              --  --  60.5                                                                              --  --  --  --  68.5                                                                              --  --  --                         HDPE 5.00                                                                             7.5                                                                              --  --  --  --  60.5                                                                              --  --  --  --  42.0                                                                              38.0                       HDPE 0.30                                                                             15.7                                                                             --  --  --  --  --  60.5                                                                              --  --  --  --  --                         LDPE 58.0                                                                             8.7                                                                              --  --  --  --  --  --  60.5                                                                              --  --  --  --                         LLDPE                                                                              1.50                                                                             11.3                                                                             --  --  --  --  --  --  --  --  42.0                                                                              --  --                         Polystyrene                                                                   PS   20    8.0 8.0 8.0 2.0 8.0 8.0 8.0 --  --  --  --                         Others                                                                        Mg alkylbenzene-                                                                         5.0 5.0 5.0 15.0                                                                              5.0 5.0 5.0 5.0 4.0 4.0 --                         sulfonate                                                                     CaCO.sub.3 25.0                                                                              25.0                                                                              25.0                                                                              5.0 25.0                                                                              25.0                                                                              25.0                                                                              25.0                                                                              50.0                                                                              50.0                                                                              50.0                       Polyethylene wax                                                                         1.5 1.5 1.5 4.0 1.5 1.5 1.5 1.5 --  --  --                         Liquid paraffin                                                                          --  --  --  --  --  --  --  --  --  --  10.0                       Ethylenebishydroxy-                                                                      --  --  --  --  --  --  --  --  --  --  2.0                        stearic acid amide                                                            Na stearate                                                                              --  --  --  --  --  --  --  --  2.0 2.0 --                         An stearate                                                                              --  --  --  --  --  --  --  --  2.0 2.0 --                         Cleanability test                                                             Cylinder temp. (°C.)                                                              230 230 230 300 230 230 230 230 230 230 230                        Preceding resin                                                                          ABS ABS ABS modi-                                                                             ABS ABS ABS ABS ABS ABS ABS                        (color)    (black)                                                                           (black)                                                                           (black)                                                                           fied                                                                              (black)                                                                           (black)                                                                           (black)                                                                           (black)                                                                           (black)                                                                           (black)                                                                           (black)                                           PPO                                                                           (black)                                                Cleaning resin                                                                           PP  PP  PP  PET PP  PP  PP  PP  PP  PP  PP                         Amount of cleaning                                                                       100 120 120 260 400 520 500 360 460 840 420                        resin used (g)                                                                Number of shots                                                                          5   6   6   13  20  26  25  18  23  42  21                         Cleaning time (min)                                                                      10  11  11  19  25  31  25  23  28  47  26                         __________________________________________________________________________

EXAMPLE 5

A high density polyethylene (melt index (JIS K6760): 0.30, Q value: 6.7,density: 0.945) (3.45 Kg), magnesium dodecylbenzenesulfonate (0.75 Kg),CaCO₃ (0.50 Kg) and a polyethylene wax (number average molecular weight:1,500) (0.30 Kg) were fed into a 20 l capacity Henschel mixer(tradename), followed by mixing these with stirring at a revolutionnumber of 500 rpm for 3 minutes, feeding the resulting mixture into thehopper of a single-screw extruder of 35 mm in cylinder diameter,extruding strands under conditions of a cylinder temperature of 200° C.and a die temperature of 210° C. and cutting the strands by means of apelletizer to obtain a granular cleaning resin composition.

Using this cleaning resin composition, an injection molding machinedirtied by an ABS resin containing 1% by weight of carbon black wassubjected to a cleanability test. The cleaning resin composition(described immediately above) was fed into the molding machine at acylinder temperature of 230° C. to clean the inside of the moldingmachine, followed by carrying out a substitution cleaning of the insideof the molding machine with a polypropylene (PP) as a cleaning resin.The quantity of the PP required therefor was 80 g (4 shots) and the timerequired for the cleaning was 9 minutes.

EXAMPLE 6

A high density polyethylene (melt index: 0.30, Q value: 6.7, density:0.945) (4.25 Kg), calcium dodecylbenzenesulfonate (0.40 Kg), silica(average particle diameter: 3.5μ or less) (0.20 Kg) and a polyethylenewax (number average molecular weight: 1,500) were mixed together underthe same conditions as in Example 5, followed by pelletization to obtaina granular cleaning resin composition. Using this cleaning resincomposition, an injection-molding machine dirtied by a black modifiedpolyphenylene oxide (PPO) containing 1% by weight of carbon black wassubjected to a cleanability test. The cleaning resin composition wasthen fed into the molding machine at a cylinder temperature of 300° C.to clean the inside of the molding machine, followed by carrying outsubstitution cleaning of the inside of the molding machine with apolyethylene terephthalate (PET) as a cleaning resin. The quantity ofthe polyethylene terephthalate as a cleaning resin required therefor was280 g (14 shots) and the time required for the cleaning was 19 minutes.

EXAMPLE 7

A high density polyethylene (melt index: 0.80, Q value: 9.2, density:0.945) (2.95 Kg), sodium dodecylbenzenesulfonate (0.90 Kg), apolyethylene wax (number average molecular weight: 1,500) (0.25 Kg) andCaCO₃ (0.90 Kg) were mixed together under the same conditions as inExample 5, followed by pelletization. Using the resulting cleaning resincomposition, a cleanability test was carried out in the same manner asin Example 5. The quantity of a polypropylene used as a cleaning resinwas 140 g (7 shots) and the time required for the cleaning was 12minutes.

EXAMPLE 8

A high density polyethylene (melt index: 0.80, Q value: 9.2, density:0.945) (4.05 Kg), potassium dodecylbenzenesulfonate (0.20 Kg), MgCO₃(0.30 Kg) and a polyethylene wax (number average molecular weight:1,500) (0.45 Kg) were mixed together under the same conditions as inExample 5, followed by pelletization. Using the resulting cleaning resincomposition, a cleanability test was carried out in the same manner asin Example 5. The quantity of a polypropylene used as a cleaning resinwas 120 g (6 shots) and the time required for the cleaning was 11minutes.

EXAMPLE 9

A high density polyethylene (melt index: 0.30, Q value: 6.7, density:0.945) (3.70 Kg), magnesium dodecylbenzenesulfonate (0.45 Kg), MgCO₃(0.65 Kg) and a polyethylene wax (number average molecular weight:1,500) (0.20 Kg) were mixed together under the conditions as in Example5, followed by pelletization. Using the resulting cleaning resincomposition, a cleanability test was carried out in the same manner asin Example 6. The quantity of polyethylene terephthalate (PET) used as acleaning resin was 240 g (12 shots) and the time required for thecleaning was 17 minutes.

COMPARATIVE EXAMPLE 8

A high density polyethylene (melt index: 0.70, Q value: 13.2, density:0.945) (3.45 Kg), magnesium dodecylbenzenesulfonate (0.75 Kg), CaCO₃(0.50 Kg) and a polyethylene wax (number average molecular weight:1,500) (0.30 Kg) were mixed together under the same conditions as inExample 5, followed by pelletization. The resulting cleaning resincomposition was subjected to a cleanability test in the same manner asin Example 5. The quantity of a polypropylene used as a cleaning resinwas 440 g (22 shots) and the time required for the cleaning was 27minutes.

COMPARATIVE EXAMPLE 9

A high density polyethylene (melt index: 2.20, Q value: 8.4, density:0.945) (3.45 Kg), magnesium dodecylbenzenesulfonate (0.75 Kg), CaCO₃(0.50 Kg) and a polyethylene wax (number average molecular weight:1,500) (0.30 Kg) were mixed together under the same conditions as inExample 5, followed by pelletization. Using the resulting cleaning resincomposition, a cleanability test was carried out in the same manner asin Exmaple 5. The quantity of a polypropylene used as a cleaning resinwas 580 g (29 shots) and the time required for the cleaning was 34minutes.

COMPARATIVE EXAMPLE 10

A linear low density polyethylene (melt index: 2.50, Q value: 13.0,density: 0.920) (2.50 Kg), sodium dodecylbenzenesulfonate (0.50 Kg),talc (2.30 Kg), sodium stearate (0.10 Kg) and zinc stearate (0.10 Kg)were mixed together under the conditions as in Example 5, followed bypelletization. Using the resulting cleaning resin composition, acleanability test was carried out in the same manner as in Example 5.The quantity of a polypropylene used as a cleaning resin was 680 g (34shots) and the time required for the cleaning was 39 minutes.

The compositions and the results of the cleanability tests of Examples5-9 and Comparative examples 8-10 are collectively shown in Table 2.

                                      TABLE 2                                     __________________________________________________________________________               Example             Comparative example                            Item       5   6   7   8   9   8   9   10                                     __________________________________________________________________________    Composition (wt. %)                                                           PE   MI Q                                                                     HDPE 0.30                                                                              6.7                                                                             69.0                                                                              85.0                                                                              --  --  74.0                                                                              --  --  --                                     HDPE 0.80                                                                              9.2                                                                             --  --  59.0                                                                              81.0                                                                              --  --  --  --                                     HDPE 0.70                                                                             13.2                                                                             --  --  --  --  --  69.0                                                                              --  --                                     HDPE 2.20                                                                              8.4                                                                             --  --  --  --  --  --  69.0                                                                              --                                     LLDPE                                                                              2.50                                                                             13.0                                                                             --  --  --  --  --  --  --  50.0                                   Neutral salt of alkyl-                                                                   15.0                                                                              8.0 18.0                                                                              4.0 9.0 15.0                                                                              15.0                                                                              10.0                                   benzene sulfonic acid                                                         Inorganic filler                                                              CaCO.sub.3 10.0                                                                              --  18.0                                                                              --  --  10.0                                                                              10.0                                                                              --                                     MgCO.sub.3 --  --  --  6.0 13.0                                                                              --  --  --                                     Talc       --  --  --  --  --  --  --  46.0                                   Silica     --  4.0 --  --  --  --  --  --                                     Polyethylene wax                                                                         6.0 3.0 5.0 9.0 4.0 6.0 6.0 --                                     Na stearate                                                                              --  --  --  --  --  --  --  2.0                                    An stearate                                                                              --  --  --  --  --  --  --  2.0                                    Cleanability test                                                             Test temp. (°C.)                                                                  230 300 230 230 300 230 230 230                                    Preceding resin                                                                          ABS PPO ABS ABS PPO ABS ABS ABS                                    (color)    (black)                                                                           (black)                                                                           (black)                                                                           (black)                                                                           (black)                                                                           (black)                                                                           (black)                                                                           (black)                                Cleaning resin (color)                                                                   PP (N)                                                                            PET PP (N)                                                                            PP (N)                                                                            PET PP (N)                                                                            PP (N)                                                                            PP (N)                                                (N)         (N)                                                Quantity of cleaning                                                                     80  280 140 120 240 440 580 680                                    resin used (g)                                                                Cleaning time (min)                                                                      9   19  12  11  17  27  34  39                                     Number of shots                                                                          4   14  7   6   12  22  29  34                                     __________________________________________________________________________     Note                                                                          HDPE: high density polyethylene                                               LLDPE: linear low density polyethylene                                        N: natural color                                                         

The cleaning resin compositions of the present invention exhibit a farsuperior cleaning effect upon cleaning of molding machines at the timeof grade exchange in plastic molding processing.

By using the cleaning resin composition of the present invention, it ispossible to notably reduce the quantity of the succeeding cleaning resinused and it is also possible to far shorten the time required for thecleaning, as compared with the case of using conventional cleaning resincompositions. For example, when the preceding ABS resin is exchangedwith polypropylene, it is possible to reduce the quantity of thepolypropylene used, required for succeeding cleaning, down to 1/3 orless and it is also possible to shorten the cleaning time down to 1/2 to1/3 or less.

Further, even when engineering plastics molded at high temperatures suchas modified polyphenylene oxide are the preceding resin, the cleaningresin composition of the present invention exhibits a notable cleaningeffect at the time of color exchange and resin exchange.

What we claim is:
 1. A cleaning resin composition having 1 to 10% byweight of a polystyrene resin, 1 to 20% by weight of a neutral salt ofan alkylbenzenesulfonic acid, 1 to 30% by weight of an inorganic fillerand 0.5 to 10% by weight of a water-repellent compound, blended with ahigh density polyethylene resin having a melt index of 1.0 or less and aQ value expressing a molecular weight distribution, of 10 or less, thetotal % by weight of said composition being
 100. 2. A cleaning resincomposition according to claim 1 comprising a melt-kneaded and moldedpellet.